The present invention relates to a biosensor for analyzing a specific component in a liquid sample and, more particularly, to a biosensor having a cavity into which a liquid sample is drawn by capillary phenomenon.
As a biosensor for analyzing a specific component in a liquid sample, there is, for example, a biosensor for detecting a blood sugar level or the like by measuring a current value that is obtained by a reaction between glucose in blood and a reagent such as glucose oxidase or the like which is held in the sensor.
FIG. 4 is an exploded perspective view illustrating a conventional biosensor for measuring a blood sugar level as described above.
In FIG. 4, a working electrode 1 and a counter electrode 2 are formed by printing on an insulating support 5 comprising polyethylene terephthalate or the like, a reagent layer 10 including glucose oxidase and an electron acceptor is formed on the working and counter electrodes 1 and 2 and, further, a surfactant layer 11 comprising yolk lecithin or the like is formed on the reagent layer 10.
Furthermore, on the surfactant layer 11, a spacer 7 having a long and narrow cut-out portion on the electrodes and the reagent layer 10, and a cover 6 having an air hole are bonded together onto the insulating support 5 so as to form a cavity 12 in which a specific amount of sampled blood is made to react with the reagent layer 10, and a current value that is generated by such a reaction is detected with the working and counter electrodes 1 and 2.
In the biosensor constructed as described above, blood is drawn from a suction inlet 8 into the cavity 12 by capillary phenomenon, and is guided to the position where the electrodes and the reagent layer 10 are presently located. Then, a current value that is generated by a reaction between the blood and the reagent on the electrodes is read by an external measuring apparatus (not shown) that is connected to the biosensor through leads 3 and 4, and a blood sugar level in the blood is obtained according to the current value.
Conventionally, when blood is applied onto the suction inlet 8 and sampled, in order to draw the blood quickly and deep into the cavity 12 by capillary phenomenon, it has been proposed that the surfactant layer 11 is spread so as to cover the reagent layer 10.
However, in the conventional biosensor which facilitates the drawing of blood into the cavity 12 by providing the surfactant layer 11 over the reagent layer 10, since the blood is drawn into the cavity 12 while dissolving the surfactant layer 11 and, further, since the blood reacts with the reagent layer 10 on the electrodes 1 and 2 while dissolving the reagent layer 10, the surfactant layer 11 prevents the reagent layer 10 from dissolving into the blood, and this causes variations in the sensitivity of the sensor or in the measured value, thereby resulting in a detrimental effect on the performance of the sensor.
Further, in the construction of the conventional biosensor, after the reagent layer 10 is formed by spreading a solution including glucose oxidase and an electron acceptor over the electrodes and then drying the solution, the formation of the surfactant layer 11 on the reagent layer 10 requires a step of applying and spreading a solution including a surfactant so as to cover the reagent layer 10, and a step of drying the surfactant layer. Therefore, the process of manufacturing the biosensor takes a much greater time, which results in poor productivity.
The present invention is made to solve the above-described problems. An object of the present invention is to provide a biosensor which can promote the flow of blood into the cavity so as to quickly and sufficiently draw the blood into the cavity without forming a surfactant layer on the reagent layer.
According to a first aspect of the present invention, in a biosensor which is provided with a cavity into which a liquid sample is drawn by capillary phenomenon and which is able to analyze a component in the liquid sample by a reaction between the drawn liquid sample and a reagent, the surface itself of at least a portion of side walls of the sensor facing the cavity has hydrophilicity.
According to the biosensor constructed as described above, since at least a portion of the side walls of the sensor, which side walls face the cavity into which the liquid sample is drawn by capillary phenomenon, has hydrophilicity at its surface, suction of the liquid sample can be promoted without providing a surfactant layer on the reagent that reacts with the liquid sample. Accordingly, the process of manufacturing the sensor can be simplified.
According to a second aspect of the present invention, in accordance with the biosensor of the first aspect, the side walls of the sensor facing the cavity are made of a resin material in which a surfactant is mixed.
According to the biosensor constructed as described above, since the side walls having hydrophilicity are made of a resin material in which a surfactant is mixed, suction of the liquid sample can be promoted without providing a surfactant layer on the reagent that reacts with the liquid sample, and the process of manufacturing the sensor can be simplified.
According to a third aspect of the present invention, in accordance with the biosensor of the second aspect, the amount of the surfactant to be mixed is 0.01 weight % or more of the resin material.
According to the biosensor constructed as described above, since the side walls of the sensor facing the cavity are made of a resin material into which a surfactant of 0.01 weight % or more of the resin material is mixed, a sufficient blood suction promoting effect can be achieved.
According to a fourth aspect of the present invention, in accordance with the biosensor of the first aspect, the side walls of the sensor facing the cavity are made of a film whose surface is covered with a surfactant.
According to the biosensor constructed as described above, since the side walls of the sensor having hydrophilicity are made of a film whose surface is covered with a surfactant, suction of the liquid sample can be promoted without providing a surfactant layer on the reagent that reacts with the liquid sample and, accordingly, the process of manufacturing the sensor can be simplified.
According to a fifth aspect of the present invention, in accordance with the biosensor of the first aspect, the side walls of the sensor facing the cavity are made of a film whose surface is covered with a resin having a hydrophilic polar group.
According to the biosensor constructed as described above, since the side walls of the sensor having hydrophilicity are made of a film whose surface is covered with a resin having a hydrophilic polar group, suction of the liquid sample can be promoted without providing a surfactant layer on the reagent that reacts with the liquid sample and, accordingly, the process of manufacturing the sensor can be simplified.
According to a sixth aspect of the present invention, in accordance with the biosensor of the fourth or fifth aspect, the thickness of the surfactant or the resin having a hydrophilic polar group, which covers the film, is several tens of angstroms or more.
According to the biosensor constructed as described above, since the side walls of the sensor facing the cavity are made of a film that is covered with the surfactant or the resin having a hydrophilic polar group, a sufficient blood suction promoting effect can be achieved.
According to a seventh aspect of the present invention, in accordance with the biosensor of the first aspect, the surface of at least a portion of the side walls forming the cavity is chemically reformed.
According to the biosensor constructed as described above, since the surface of at least a portion of the side walls forming the cavity is chemically reformed so as to form the side walls of the sensor having hydrophilicity, suction of the liquid sample can be promoted without providing a surfactant layer on the reagent that reacts with the liquid sample, and accordingly, the process of manufacturing the sensor can be simplified.
According to an eighth aspect of the present invention, in accordance with the biosensor of the seventh aspect, a hydrophilic functional group is formed on the surface of at least a portion of the side walls facing the cavity by subjecting the surface to any of the following treatments: plasma discharge, coupling reaction, ozone treatment, and UV treatment.
According to the biosensor constructed as described above, the surface of at least a portion of the side walls forming the cavity is subjected to any of the following chemical surface treatments: plasma discharge, coupling reaction, ozone treatment, and UV treatment, thereby forming a hydrophilic functional group on the surface. Therefore, the surface of at least a portion of the side walls facing the cavity can have hydrophilicity.
According to a ninth aspect of the present invention, in accordance with the biosensor of the first aspect, the surface of at least a portion of the side walls facing the cavity is made of a rough surface.
According to the biosensor constructed as described above, since the surface of at least a portion of the side walls forming the cavity is roughened so as to form the side walls of the sensor having hydrophilicity, suction of the liquid sample can be promoted without providing a surfactant layer on the reagent that reacts with the liquid sample, and, accordingly, the process of manufacturing the sensor can be simplified.
According to a tenth aspect of the present invention, in accordance with the biosensor of the ninth aspect, a rough surface is formed at the surface of at least a portion of the side walls facing the cavity by subjecting the surface to any of the following treatments: sand blasting, electric discharge, non-glare treatment, mat treatment, and chemical plating.
According to the biosensor constructed as described above, the surface of at least a portion of the side walls forming the cavity is subjected to any of the following treatments: sand blasting, electric discharge, non-glare treatment, mat treatment, and chemical plating, thereby forming a rough surface. Therefore, the surface of at least a portion of the side walls facing the cavity can have hydrophilicity.
According to an eleventh aspect of the present invention, in accordance with the biosensor of any one of the first through tenth aspects, the surface of the support, on which the reagent that reacts with the liquid sample is formed, also has hydrophilicity.
According to the biosensor constructed as described above, not only the surface of at least a portion of the side walls forming the cavity but also the surface of the support on which the reagent that reacts with the liquid sample is formed, have hydrophilicity. Therefore, the area of the portion having hydrophilicity in the side walls facing the cavity is increased, whereby the liquid sample can be drawn with higher efficiency.
According to a twelfth aspect of the present invention, in accordance with the biosensor of any one of the first through tenth aspects, the surface of the support on which electrodes that detect the reaction between the liquid sample and the reagent are formed also has hydrophilicity.
According to the biosensor constructed as described above, not only the surface of at least a portion of the side walls forming the cavity but also the surface of the support on which the electrodes for detecting the reaction between the liquid sample and the reagent are formed have hydrophilicity. Therefore, the adhesion of the electrodes to the support on which the electrodes are formed is improved, and the problem of electrode peeling is solved, whereby the reliability of the sensor is improved.
According to a thirteenth aspect of the present invention, in accordance with the biosensor of the twelfth aspect, the surface of the support is made of a rough surface, and the level of the rough surface to be formed is 0.001 xcexcm to 1 xcexcm.
According to the biosensor constructed as described above, since a rough surface having unevenness in a level from 0.001 xcexcm to 1 xcexcm is formed at the surface of at least a portion of the side walls of the sensor facing the cavity, the adhesion is improved.